9. Interpretation of Airphotos for Soil Mapping and Land Evaluation.

211 9. INTERPRETATION OF AIRPHOTOS FOR SOIL MAPPING AND LAND EVALUATION

Airphoto-interpretation is the common aid for soil mapping.

In aerial

photography, there is no limitation for scale. Aerial photography not only offers information on relief and slope but also makes a lot of other applications possible.

However, because of changing weather conditions and cloud

cover, the number of flight days is usually limited, and a repetitive coverage throughout the year is generally n o t economic. The spectral resolution is limited to the range between 0.12

pm

and 0.9

pm,

which is Ultraviolet, Visible and Near Infrared. Aerial photography generally operates in the Visible zone, but more and more application is found of Near Infrared sensitive films e.g.

Black- and White-Infrared and False Colour. For

the different aspects on aerial photography and physiographic interpretation, the reader is also referred to the preceding chapters 4 up to and including 8. Plants are strong reflectors of Near Infrared, and different vegetation cover types often show a different reflectance. Good results can be mentioned with regard to the use of false colour-film in agricultural and ecological studies, in differentiating between vegetation cover types, and in locating vegetation areas affected by disease. Due to its successful application, airphoto-interpretation has become a

generally accepted aid for soil survey during the past thirty years.

An

evaluation of various remote sensing techniques in northern Canada, taking into account visual interpretation together with computerized classification of remotely sensed data, revealed that airphoto-interpretation provided the best cost and data-effective method for ecological land classification. Mapping of soils, landforms and landtypes was best accomplished with the aid of airphotos.

It was

suggested

complementary way

that (Thie,

other remote sensing means

1976).

However,

SPOT-data

should be are

used

in a

competitive with

airphotos for medium-scale mapping.

9.1. Interpretation of black- and- white airphotos. Black- and white-airphotos are the most common tools in soil survey and the soil surveyor should be trained in making deductions about soil conditions through physiographic and morphogenetic interpretation. Black- and white-

212 photography is normally cost-effective in soil survey projects, provided that there are no serious limitations in obtaining flight coverage. The general feature of aerial photography in offering low-cost stereoscopy, is one of its most important advantages. Another aspect is the grey tone structure that is more friendly to the Observer than colour tones are. Especially the red and magenta colours that dominate most of the false colour imagery may fatigue the observer. Examples of airphoto-interpretation of areas in Suriname and b n i a are given in figures 9.1 to 9.4.

It should be emphasized that in the examples a

selection of aspects has taken place. The Suriname and Kenia areas have a mean annual rainfall of 2250 and 1550 mm respectively, and are representative of tropical areas with land use of respectively low and high intensity. The Suriname area (Fig. 9.1), photographed

at

a scale of

landtype/relief, land

1:40,000,

use/parcelling

may be

-

initially

studied using the aspects

natural vegetation, and

condition. The pictured area is an example of

drainage

the Young Coastal Plain

landscape, which shows in most of the area natural vegetation, since land use is

of

low

intensity

(shifting

cultivation

is

almost

absent).

Drainage

condition is concluded from site, land use and natural vegetation. A soil map (Mulders, 1977) is given in Fig. 9.2 Legend Fig. 9.2 Soil Map Northern Suriname (original scale 1:100.000): YOUNG COASTAL PLAIN 4) Poorly drained half-ripe and ripe clay; 8) Well drained medium and fine sand; Imperfectly drained sandy loam OK medium and fine sand; 9) 11) Poorly and very poorly drained nearly ripe clay; 16) Very poorly drained half-ripe (peaty) clay; 17) (Formerly) artificially drained ripe clay; 19) Very poorly drained half-ripe and unripe mostly pyritic clay and peat; Three landtypes can be distinguished, these being: the Beach Ridge Complex (8, 9 and l l ) , the Swamp and Marsh ( 4 , 16 and 19) and the River Flat ( 1 7 ) .

The different units have specific characteristics on the photographs of which natural vegetation is the most important. The Beach ridges (8) are characterized by high trees outstanding above a canopy with moderately high trees. Often the ridges can be recognized by the linear arrangement of these high trees. Where the ridges are close to each other and relatively narrow, complexes are distinguished. Between

these,

depressions are

found

with

moderately

high

forest and

213 imperfectly drained soils (9).

On other places, where the canopy in the Beach

Ridge Complex shows grass and low trees, soils are poorly to very poorly drained (11).

The Swamp and Marsh shows a unit with grass and moderate to high

coverage by low trees which contains very poorly drained mostly pyritic clay and peat (19).

During a transgression, clays are deposited in the depressions

which now bear an extremely low tree coverage (4),

or low tree coverage in the

actual drainage ways (16). The River Flat (17) was formerly used for plantations. Some of these are now used again for agriculture, others are not, and have low to moderately high forest. The area in Kenia (Fig. 9.3)

is initially photographed at a scale of 1:12.500

and may be studied by using the aspects of landtype/relief (Fig. 9.4a), site and land use/natural vegetation (fig. 9.4b). subdivision in

landtypes-relief, and when

slope,

The present scale enables a

combined with

land

use/natural

vegetation a relation to soil condition is accomplished. The results of the interpretation can be compared with the soil map of the area (fig. 9.4). Legend Landtypes - Relief (Fig. 9.4a): A. Upland ridge complex, mainly elongated: steeply dissected (As) and hilly (Ah) B. Upland hills: rolling to hilly C. Undulating plain. Legend (Fig. 9.4b): Land use

Natural vegetation

A. Agricultural use: annual herbaceous crops, pastoralism, some woody crops. P. Pastoralism.

Extr. low cov. trees and scrubs; lowmod. COV. grass.

N. Nature reserve F. Timber, firewood. Abbreviations: extr.

=

Very low - low COV. trees and scrubs; high COV. grass. Very high COV. scrubs. Riverside forest; mod.

extremely; mod.

=

moderate;

Legend soil map (Fig. 9.4~): C Chromic Luvisols and Luvic Phaeozems G Gleyic Luvisols and Gleyic Phaeozems S Solodic Planosols E Eutric and Chromic Cambisols, Haplic Phaeozems R Eutric Regosol (lithic phase)

COV. =

COV.

trees.

coverage.

Fig. 9.1 Airphoto Stereotriplet of an area in the Young Coastal Plain near Groningen at the Saramacca river (Suriname).

215

Reconnaissance S o i l Map o f N o r t h e r n Suriname n o r t h o f t h e 5 t h degree o f l a t i t u d e

e 1 km Fig.

9.2

S o i l map of

t h e area n e a r Groningen (Suriname, Map s h e e t 13).

For

legend: s e e t e x t . The a c t u a l s c a l e of t h e photographs i n Fig. relief,

9.3 o n l y e n a b l e s a s u b d i v i s i o n i n

t h e s l o p e and s i t e u n i t s b e i n g t o o small.

r a t h e r broad

s u b d i v i s i o n of

r e l i e f (Fig. 9.4a)

the land,

Although t h i s produces a

t h e i n t e r p r e t a t i o n on l a n d t y p e s and

shows a number of u n i t s which a l s o may be r e c o g n i z e d on t h e

s o i l map ( F i g . 9 . 4 ~ ) .

I n a number of

c a s e s , n a t u r a l v e g e t a t i o n and l a n d u s e p r o v i d e f o r f u r t h e r

e v i d e n c e on s o i l c o n d i t i o n s .

Compare F of Fig.

9.4b w i t h G of Fig.

n o t e t h a t R s o i l s a r e mainly used f o r p a s t o r a l i s m

9.4c,

and

(and n a t u r e r e s e r v e ) .

The comparison w i t h t h e s o i l maps shows t h a t a c l o s e r e l a t i o n between t h e combined a s p e c t i n t e r p r e t a t i o n maps and

t h e s o i l . map can be accomplished.

Normally t h e l a n d t y p e is t h e main c r i t e r i o n f o r d e s c r i p t i o n i n t h e legend of t h e i n t e r p r e t a t i o n map, and a f u r t h e r s u b d i v i s i o n may be made on t h e b a s i s of

Fig. 9.3

Airphoto Stereotriplet of an area near Rangwe (Kisii, Kenya).

217

In ? r p r e t a ion 1a n d t w e s and r i i i e f

N

e 1 km

Interpretation l a n d use and na t u r a 1 vegeta t ion

1 km

218

Soil Map

1 km

Fig. 9 . 4

Interpretation and soil map of the Rangwe area (Kisii, Kenya, Top. map 130/1) a. Interpretation landtypes and relief b. Interpretation landuse and natural vegetation C. Soil map (Breimer, 1976)

other aspects. Examples of legends are given in par. 9.2. Although qualitative methods are most relevant for soil surveys, quantitative methods may assist the interpretation and may optimize the use of the information content of the airphotos. One of the features to digitize is the tonal variation. Digitization of the density range on the film is done by using

a

computer, the output codes from the digitizer are recorded and stored for subsequent retrieval and analysis. By using a colour television monitor, colour

can

be

designated

to

certain

grey

levels

to

facilitate

the

interpretation of the images obtained. Benson et al. (1973) used computerized methods for a detailed study of a fallow field in South Dakota in order to separate eroded and non-eroded soils. In this study statistical analysis were used to determine the relationship between soil properties and the tonal variations on the airphotos. The results indicate that the tonal variation

219 evident on the photographs of the field is related to several soil properties. The eroded terrain shows light tones due to increased reflectivity of the surface soil after removal of the A horizon and exposure of the underlying calcareous parent material.

The computerized method may be valuable, for

instance, when multitemporal data have to be studied to detect the progress of erosion over a certain period of time.

9.2.

The legend of the airphoto-interpretation map

A grouping of airphoto-interpretation units may be done as follows: A, B , C, etc.

landtype in morphogenetic terms

OK

physiographic indicat-

ions such as relief classes and drainage density or pattern;

A1, A2, B1 etc. All,

A12, B l l ,

physiographic subdivision; etc.

phases, minor differences.

When the structure is very complex, additional codes may be applied for a.0. slope, natural vegetation, land use, phototone or mottling of bare surfaces. The following features may be indicated: grade

OK

density, type or shape,

size, regularity and site sequence. Slope classes provide examples of grade, e.g. classes 1-6.

For surface density

or coverage classes, the reader is referred to par. 8.5.

(see also par. 6 . 3 :

texture and structure).

These low-level codes can be read on the map. The

legend does not show the total number of mapping units as they are delineated on the map, but insight in the properties of the mapping units can be given separately. Examples I and I1 of airphoto-interpretation legends for reconnaissance survey are given below. The following remarks are made in connection with these examples. Different

landscapes may

need

different

approaches.

In

arid

areas

attention will be centred on relief, drainage pattern and phototone, while in areas with tropical rain forest (and low human activity) relief, drainage pattern and natural vegetation are diagnostic for the distribution of soils. Furthermore, each study has its own requirements, e.g.

erosion studies and

land evaluation need special emphasis on slope and land use. The level of detail is determined strongly by the scale of the airphotos

220

as well as by the physiognomy of the area. The examples are only meant as a basis

for discussion.

It is stressed that the legend of the airphoto-

interpretation map needs much emphasis, and that discussions with team members may improve it considerably. A s far as soil survey is concerned, the lowest level should clearly present the soil mapping unit, while the higher levels have their special value for land division. lowest

level in accidented

In semi-detailed surveys, the

terrain will most

often be

based

on slope

characteristics. While a number of aspects are presented in the legend on the map, a separate description is usually given of

other aspects which are not

used

for

discrimination between the mapping units. This description is given in columns (tables). The

following

requirements

are

suggested

for

legends

of

airphoto-

interpretation maps: a. the units should be ordered logically, e.g.

old to young, high to low

elevation, high to low percentage of slope; b. high

levels

generally

indicate

land

types

with

geographic

soil

associations; C.

low levels generally indicate soil series or toposequences of soils (soil catenas);

in other cases, the lowest level is a subdivison made up by

photo-technical

description

(grey

tone

or

mottling),

of

which

the

significance has to be studied in the field; d. since morphogenetic terms (e.g.

floodplains, levees or dunes) offer more

information about soil conditions, these terms are preferred to physiographic terms (based on features such as slope and relief). ad a. Proposal for arrangement of aspects and grade or density in the legends: morphography and landtype land system (or type) - land unit - land component or site, land system - relief - slope, drainage density/high to low, high to low elevation, relief/steeply dissected to flat, other aspects vegetation/forest - grass - bare, coverage/high to low, structure and texture/coarse to fine, land use/nature reserve - forestry - rangeland agricultural use - settlement and infrastructure - water, phototone/light to dark.

-

221 EXAMPLE I Legend of airphoto-interpretation map of the Kilifi-area (Kenya). Scale of panchromatic airphotos 1:50 000. A Relatively high interior upland Very low to low drainage intensity A1 Rolling land with dendritic drainage pattern All Open woodland savannah Open woodland savannah with up to 50% grazing A12 Open woodland savannah with 50-80% grazing A13 A2 "Kopjes" land (small isolated bare hills) A21 Open woodland savannah A3 Undulating land with dendritic drainage pattern A31 Open woodland savannah A32 Open woodland savannah with up to 50% grazing A33 Open woodland savannah with 50-80% grazing A4 Rivervalley land B Relatively low interior upland B1 Moderate drainage density B11 Hilly land with subparallel drainage pattern B12 Rolling land with dendritic drainage pattern Further subdivision on natural vegetation and land use R2 Low drainage density B21 Rolling land with dendritic drainage pattern B22 Undulating land with dendritic drainage pattern Further subdivision on natural vegetation and land use B3 Rivervalley land C Coastal upland C1 High drainage density C11 Rolling land with dendritic drainage pattern C12 Rolling land with pinnate drainage pattern C2 Moderate drainage density C21 Hilly land with subparallel drainage pattern C22 Rolling land with subparallel drainage pattern C23 Rolling land with dendritic drainage pattern C24 Undulating land with dendritic drainage pattern C3 Low drainage density Rolling land with subparallel drainage pattern C31 Undulating land with subparallel drainage pattern C32 Undulating land with dendritic drainage pattern C33 C4 Rivervalley land D Coastal plain and marine terraces Very low to low drainage density D1 Relatively high undulating land D11 High marine terrace D12 Medium marine terrace D13 Low marine terrace D2 Beach area D3 Estuarine land D4 Tidal creek land D41 Saline margin D42 Overflow area Note: The description in tables of other interpreted land characteristics followed by deduction on inferred aspects is not included.

222

EXAMPLE I1 Legend of airphoto-interpretation map of the Antelope (California). Scale of panchromatic airphotos 1 : 2 4 , 0 0 0 . Landtypes and subdivision

A

Area

Other aspects Drainage Drainage density pattern

Vegetation and land use

(Inferred) drainage condition

very low

dendritic

grass and herbs

well drained

A2 Steep slopes

high

parallel

A3 Hilly land

high

dendritic

A4 Rolling to hilly

moderate

dendritic

low

dendritic

moderate

parallel and

high

dendritic dichotomic

Low mountaneous land A1 High undulating

plateus

land

A5 Low, undulating

to rolling land

B

Valley

Plains B1 Sloping footslopes

B2 Gently sloping

alluvial fans B3 Flat to gently

very low dendritic

sloping plain B4 Flat to gently

sloping depressions

-

locally diffuse gully pattern

or bare trees, shrubs, grass and herbs trees and shrubs or bare

grass and herbs

excessively drained somewhat excessively drained well drained

or bare grass and herbs, well drained shrubs or bare grass and herbs

well drained

grass and herbs, well drained bare or arable land arable land, well drained grass and herbs or bare grass and herbs moderately well or arable land drained

223

9.3.

From airphoto-interpretation map to soil map

A soil survey comprises the delineation of soil bodies. This is done by the

study of soil profiles. A soil profile is a sample of a pedon, the smallest unit of soil. In practice, one uses polypedons, which comprise a number of pedons with a natural boundary. The polypedon, or natural soil body, may be homogeneous or composite with regard to soil classes or series. The units of the airphoto-interpretation map often correspond to natural and composite soil bodies. Morphogenetic units offer much information about soils, while

physiographic units

at

least offer information about soil-forming

factors or consequences of soil conditions. The airphoto-interpretation may be done before. fieldwork or interactively. In both cases, however, the airphotos have to be interpreted in order to plan the field survey. Bennema and Gelens

(1969) have treated the procedures for soil mapping with the aid of airphotos. These procedures are summarized below. The boundaries on the airphoto-interpretation map may be:

-

valid for soil survey; invalid for soil survey, since they present vegetation differences due to tillage, or envelop units which are too small for the scale of mapping;

- of questionable validity for soil survey; fieldwork is necessary to evaluate the validity. Fieldwork enables the compilation of a soil map.

It involves the following

activities: a. check on validity of boundaries; b. check on accuracy of boundaries; C.

detection of missed boundaries;

d. delineation of boundaries not visible on the airphoto; e. set-up of legend; f. profile observations for description and classification of soil. Skill is required to choose the right location of the field observations. Their position is related to soil genesis and physiography. One observation may lead to a hypothesis about the kind of soil to be expected at another place. The second or third observation may verify the hypothesis or disprove it. However, when work is getting

on,

the position of the various soils,

224

generally a repeated sequence in a landscape unit, is no longer a secret and consequently the density of the observation network generally decreases with time up to the standard minimum number of observations as guided by the publication scale. Procedures

of

fieldwork with

regard

to

validity

and

accuracy

of

boundaries are the following:

-

full check on validity and accuracy of boundaries; limited check, that is

check only on validity of questionable boundaries;

a

no check on validity and accuracy of boundaries.

The check on validity and accuracy is related to scale as follows:

-

large-scale

- medium-scale

-

small-scale

-

full check; full or limited check; limited or no check.

The total number of observations depends, apart from skill and knowledge of the surveyor, also on:

-

the scale and purpose of the survey;

- the scale and quality of the airphotos;

-

the kind of landscape. Often selected areas are studied in detail in order to obtain insight in

the kind and distribution of soil bodies. These areas are called key areas or sample areas. The study of sample areas is usually recommended, but their use is limited for:

a. relatively small areas; b. well-known landscapes; C.

detailed surveys;

d. very small scales (e.g.

1:250,000

and smaller).

The requirements for sample areas are: a. they should be samples of large areas with different mapping units, which means that they should include many soil units; b. they should be well accessible; C.

there is a need for more than one sample area for large units.

Procedures with sample areas:

-

selection of sample areas by

indication of

major

landscape units

airphoto-interpretation;

-

detailed airphoto-interpretation of sample areas (indication of land

in

225

components);

A

survey of sample areas; airphoto-interpretation of total area; check on validity and accuracy in total area. revision of

the airphoto-interpretation of

the total area is usually

necessary due to evidence from field observations. Tropical forests are almost inaccessible and consequently need specific methods for soil mapping. Field observations are done in transects and in sample areas which have a relative dense network of transects. Soil mapping boundaries

are

drawn

by

interpolation

between

the

extrapolation outward from the areas with transects.

transects

and

by

It is important to

realize that remote sensing images, including airphotos, are the only tools for mapping in tropical forests. Often the remote sensing tool determines the possible detail. That is, when the interpretation units have shown their validity as indicators of soil units, the soil surveyor often has only the opportunity to map and describe the contents of these interpretation units. This implies that the final map may comprise homogeneous units as well as heterogeneous units (soil complexes).

This statement is made, since the

delineation of boundaries not visible

the remote sensing imagery, generally

on

requires much field work and thus time and financial means, which may be out of the scope of the project. S o i l variability may be studied in the field by statistical methods (see:

Webster, 1977; Northcliff, 1978; Burrough and Kool, 1981). An example of a possible soil survey using modern techniques like the statis-

tical approach i n conjunction with airphoto-interpretation is the following. On

the basis of the airphoto-interpretation, mapping units are selected which

show a trend in geographical distribution; these units are studied in detail either by transects or by sample areas. The variability within the units and between the units is analysed statistically, in order to check the validity of the discriminating criteria used to delineate the boundaries between the mapping units as well as the variation within the units. This might give an indication of the validity of the mapping units and may offer an indication of the number

of

observations necessary to map

the units accurately. The

statistical approach is particularly useful in case of large mapping units, which appear on the interpretation map as homogeneous units

on

the basis of

226 the criteria used. In the field, sampling together with statistical analysis might reveal diagnostic soil characteristics, which can be used for a further subdivison into soil units as well as for description of soil complexes, and, as stated before, to direct the number of field observations needed for an accurate description of the mapping units. The legend of the airphoto-interpretation map has to be transformed into a legend for the soil map. This can be done by a translation of physiography and morphography into morphogenesis followed by indication of soil taxonomic units. There are two types of soil map legends: a.physiography

and morphogenesis at high level (e.g.

soils of the rolling uplands),

river levees soils,

followed by taxonomic units, such as soil

series (or higher levels) and phases, the latter generally pragmatic (land use directed) ; b.taxonomic

units, e.g.

orders, suborders, great groups, etc.;

associated

soils should be indicated too.

9.4.

Land evaluation and planning of field survey A fundamental approach to land evaluation has been defined in its initial

stage by Beek and Bennema in 1971, and on the Expert Consultation of Land Evaluation for Rural Puposes at Wageningen (The Netherlands) in October 1972 (Brinkman and Smyth ed.,

1973). The first draft of a framework by FA0 (1973)

was widely circulated with a request for comments. This resulted in 1976 in "A Framework for Land Evaluation". Land

evaluation involves the execution and

interpretation of basic

surveys of climate, soil, vegetation and other aspects of land in terms of the requirements of kinds of land use or LUTS. To be of value for planning, the LUTS to be considered have to be limited to those which are relevant within the physical, economic and social context of the area and its population. Interpretation of remote sensing imagery gives information on soils, vegetation, present land use, and to a limited degree on climatic conditions. Also the physical effects of economic and social factors may be visible to some extent. Their information content and synoptic view cause remote sensing data to be important aids in land evaluation. A preliminary evaluation based

221 on

interpretation results of remote sensing data may be considerably helpful

in the planning. Airphoto-interpretation is applicable for delineation of land

mapping units being characterized by basic, compound and inferred aspects. These aspects are in fact land characteristics. The ultimate estimation of the grade of land qualities is only possible after a proper weighing of the land characteristics that influence the land qualities.

In

using

such

interpreted

land

characteristics and

expected

land

qualities and suitability, it has to be kept in mind, that it is only an interpretation, being of value for the planning of field survey. The best score will be obtained in S 1 (highly suitable) and N (not suitable) classes. Field and laboratory data are decisive for the final suitability but the preliminary interpretation may direct the field survey to areas that are expected to be suitable for the intended use already at an early stage of the survey. Some land characteristics such as relief grade, slope grade, slope length, site and drainage density may well be estimated by aerial photointerpretation and may direct the field survey to the most promising areas. Inferred interpretation aspects are of considerable value. requires a

specific approach in deduction.

As

Each of them

an example, the erosion

condition is discussed. The

methodology

of

airphoto-interpretation

for

erosion

and

soil

conservation survey is comparable with that for soil survey. However, special emphasis is laid upon aspects, such as:

-

relief and slope (angle, shape, length and position); drainage pattern and density;

-

-

erosion features; location of severely eroded land

8.0.

badland;

grey tone pattern; microrelief and surface stoniness; site a.0.

relative position of accumulation and erosion surfaces;

land use and crops, parcelling; percentage of vegetation cover; percentage o f fallow land and abandoned arable land; cattle tracks; size-, shape- and position of man-made terraces and other conservation

228

measures. Examples of soil erosion-accumulation sequences based on grey tone pattern on airphotos from top- slope- valley bottom (Bergsma, 1974) are:

-

the common case dark

-

light

-

dark, where the A - horizon on the slopes

is largely eroded and a lighter s u b s o i l is exposed;

-

the reverse case light - dark

-

light, where a light textured surface

soil on the slopes is largely eroded and a heavier subsoil (e.g.

an

argillic horizon) is exposed. It will be clear, that the appearance of the area itself, and scale of the airphotos determine to a large extend the potential of the interpretation. Furthermore, the information level in the form of maps and reports on environmental conditions has also much impact. However, it is important that at the start of the interpretation procedures the final aim of the project is considered. The purpose of the survey determines a.0.:

-

the kind of environmental data to be collected;

-

the required survey scale.

the minimum area of planning interest;

The latter also depends on existing base maps and other environmental data.

For practical reasons, the working or survey scale is in general larger e.g. twice the scale intended for the final maps. For planning of the field survey, three land qualities are important, these being:

-

the size, distribution and arrangement of mapping units or the land complexity;

-

the trafficability expressed by

relief, drainage condition and the

presence of roads and tracks, navigable rivers and streams;

-

the accessibility of

the terrain expressed by

type and degree of

vegetation cover and the possibility of housing and/or campsites. The land complexity is scale dependent. Land may appear homogeneous at large

scales, but heterogeneous at small scales. A measure for land complexity is the size of the land component or the mapping unit at the lowest l e v e l (e.g.

All, A12). land

If the size of the components is dominantly smaller than 1 cm2, the

is considered to be heterogeneous at

the particular scale and an

229

observation density is suggested of at least 2 augerings per cm2 (final map). Table 9.1.

presents estimates of the daily number of auger observations (Nt),

and progress by soil augering in ideal terrain, which is homogeneous at scales larger than 1:100.000,

having slopes not steeper than 16 % and a tree and

shrub coverage of less than 25 %. This table is based on the following assumptions:

-

When there is a check on accuracy, the following reduction factors have to be applied i n order to calculate the number of augerings contributing to the daily progress, 0.75 for 1:5000 scale, full check; 0.70 for 1:10.000 scale, full check;

0.85 for 1:ZO.OOO scale, limited check; 0.80 for 1:50.000 scale, limited check;

-

the land is considered to be heterogeneous at scales of 1:lOO.OOO smaller (Np

-

=

and

Nt);

at scales of 1:lOO.OOO and smaller, no check on accuracy is performed, but more time is spent on transport and desk work.

The number of survey team days can be calculated by dividing the total surface area by the daily progress. In addition, the terrain characteristics have to be evaluated to obtain correct estimates for the land under consideration. The following classes of trafficability are suggested: a) well drained flat, undulating to rolling terrain; effective transport by vehicles is possible in the field; b) as for (a); no effective use of vehicles; main transport on foot; c) well drained, or excessively drained hilly to steeply dissected terrain; use of vehicles is moderately effective; d) as for (c), but no effective use of vehicles; transport on foot; e) excessively drained mountainous terrain

OL

effective use of vehicles; transport on foot.

poorly drained terrain; no

Table 9.1

Approximation of d a i l y p r o g r e s s i n i d e a l t e r r a i n u s i n g e s t i m a t e s of a u g e r i n g s / h r ( 6 f o r 1: 5.000 s c a l e , 5,9 f o r o t h e r s c a l e s ) .

Kind of s u r v e y

range of scales

scale

area survey method 1 cm2 map (S)

detailed

1:10,000 and larger

1:5,000 1:10,000

0.25 ha r e g u l a r g r i d 1/2 hr 1 ha or f r e e grid d i r e c t e d by physiography; interpolation and f u l l check on a c c u r a c y

semi-detailed

smaller t h a n 1 :10,000 up t o 1:25,000

1.20,OOO

4.0

reconnaissance

smaller t h a n 1:25,000 up t o 1:100,000

1:50,000 25.0 ha key a r e a s and 1 1 / 4 h r 1:100,000 1 km2 transects; 14 h r extra-polation, no check on accuracy

smaller t h a n 1:100,000 up t o 1: 250,000

1:200,000 4 km2

medium i n t e n s i t y

reconnaissance low i n t e n s i t y

-

ha

f r e e g r i d of transects d i r e c t e d by physiography; interpolation and l i m i t e d check on accuracy

as f o r 1: 100.000

N t = N t o t a l , N a = N a c c u r a c y check, Np = N p r o g r e s s = Nt

-

N,

average t i m e per day s p e n t at transport

1 hr

1 3/4 h r

daily transport,

d a i l y deskwork and

average time p e r day s p e n t a t desk work

average d a i l y number of auger o b s e r v a t i o n s (N) Nt Na Np

average daily progress surface area (P)

1 hr

39

10

29

7.25 ha

14 hr

32

5

27

108 ha

1 3/4 h r 2 1/4 h r

30 25

-

6

24 12

600 ha 12 km2

2 j hr

21

-

10

40 km2

N 0

231 The following classes of accessability are suggested, based on vegetation cover:

- 25 X, 25 - 75 X, 75 - 100 %.

A) tree and shrub coverage 0

B) tree and shrub coverage C) tree and shrub coverage

Reduction factors on the average daily number of auger observations have to be applied

for trafficability and accessibility in relation to

scale. The

following factors are suggested: for scales of 1:lO.OOO trafficability

and larger

c 0.90

accessibility

d 0.85 e

B 0.90

C 0.85

0.80

for scales smaller than 1:lO.OOO

same reduction factors, but in addition for

transportability or the use of vehicles in the field, these factors being: b 0.90 Table 9.2.

d

+e

0.85

gives a summary on terrain classes and reduction factors. Of

course, further testing on the reduction factors is necessary and ought to be done according to the specific conditions in land or country. Table 9.2 Terrain classes and reduction factors on average daily number of auger observations and average daily progress. terrain classes

1 2 3

4 5 6 7

8 9 10 11 12 13 14 15

trafficability average daily

a a a b b b

accessibility

A

B C A

B C

C C

A B

C

C

d d d e e

e

A

B C

A

B C

reduction factors on number of auger observations and daily progress 1 :10.000 smaller and than larger 1 :10.000

-

-

0.90 0.85

0.90

-

0.85 0.90

0.90

0.81

0.85

0.77 0.90 0.81 0.77 0.72 0.65 0.61 0.68 0.61 0.58

0.90

0.81 0.77 0.85 0.76 0.77 0.80 0.72 0.68

Through application of the reduction factors it is then possible to calculate

232 the daily number of auger observations and the corresponding daily progress, which are both dependent on the terrain characteristics. The calculation suggested is based on ideal climatic conditions or in other words, a dry season. When the field work is carried out in a wet season, another reduction factor should be applied e.g.

0.7

or 0.8.

The following formula may be used to calculate Np for terrain class x (or Npx) : Npx

=

(9 - 1)

c.s.zx.Npl

where Npl is Np for ideal terrain class 1 (see table 9.1),

-

c

=

and

reduction factor land complexity (heterogeneous terrain 0.5, homogeneous terrain 1; in table 9.1, c is applied for 1:100.000 and 1:200.000);

-

s =reduction factor for climatic conditions, wet season 0.7

or 0.8, dry

season 1;

-

Zx= reduction factor for terrain class x (see table 9.2).

The average daily progress in ha or km2 ( P ) can be calculated from: P

=

Npx

where S

.S =

(9

-

2)

area 1 cmL map (ha or kmL) at scale of publication.

Besides for auger observations, days have to be included for field work in connection with:

- preparation and detailed examination of soil pits (depth 1.5 - 2.0 m or to an impenetrable layer); average 2/day,

- deep borings ( 3

-

5 m or to an impenetrable layer) in a free grid or

preferably along transects in order to obtain insight in soil depth, parent material and in sedimentology. Soil

samples

for

laboratory

analysis

are

usually

taken

from

characteristic soil pits (typical soil profiles) throughout the area and if applicable from the key or sample areas. Sampling is done from soil horizons and/or stratifications or at regular intervals in the soil profile. In special cases, a relatively large number of samples is taken for limited laboratory analysis, often at fixed sampling depths e.g.

for estimation of salinity and/or alkalinity. Depending on the

type of survey and the information required, certain field experiments (like

233 measurements of permeability and infiltration rate and conductivity) are to be executed as well. The amount of time involved in laboratory analysis varies greatly with

the type of

analysis (soil chemical, soil physical and

OK

mineralogical) and of course the size and quality of the laboratory to which the samples are forwarded. An estimate of the rate of progress for soil sample analysis has to be made in consultation with the laboratory. Geostatistical approaches (non-aligned sampling

OK

detailed along transects)

may be used to determine soil variability and discriminating criteria between soil units. As

stated before, the purpose of study may direct and concentrate the

observations on the more "promising" parts of the area. Consequently, some land units may be studied in less detail than the rest of the area, and estimates for smaller scale may be used to calculate the work involved. Such differences in survey intensity have to be indicated checklist

on

on

the map and in the report. A

the planning of soil survey is given in table 9 . 3 .

Table 9 . 3 Checklist on the planning of soil survey.

I

survey team days Organization and Administration

I1

Preliminary airphoto-interpretation mapping units: A, B , C, etc. complexity: trafficability: accessibility: housing, campsite: transport in field:

111

Purpose of field survey: areas of high interest: minimum area of planning interest: kind of environmental data to be collected: required final scale: working scale: basic field equipment for soil sampling, soil description and mapping:

IV

Field survey expected weather conditions in survey-period: observation system(s): surface areas of land units: number of man days involved: - for geostatistical observation: - item for deep augering:

234

-

item for soil pits: item for routine augering per land unit: delay due to social or religious aspects:

V

Survey team days for other observations directed by the purpose of study other observations:

VI

Final airphoto-interpretation

VII

Laboratory analysis - samples of soil pits - other samples

VIII Preparation of maps and report

-

man-days

soil scientific work: typing: drawing: other activities

The data listed in table 9 . 3 enable the production of a time-schedule for

the soil survey. A final evaluation involves a calculation of cost of the survey. The attempt

for planning of field survey, needs further application. Good results were obtained using this method in recalculation of man-days needed for medium and small-scale soil surveys in Suriname and Pakistan. A soil map should always be accompanied by a report. An example of the contents

of a soil survey report, which may comprise the following subjects, is given below: 1)

2)

3)

4)

Introduction. Purpose of study Location of the area Material and methods. Topographic maps Geological maps Data airphotos: scale, flying height, focal distance, aerial film and camera, filters Methods of interpretation and fieldwork General information on soil forming factors in the study area. Climate Geology, geomorphology, petrology Hydrology Natural vegetation and land use Airphoto-interpretation and fieldwork. Relation between soils and soil forming factors Relation of photo-interpretation aspects with s o i l conditions Construction of legend

235 5)

6)

7) 8)

9.5.

Soil data and classification. Description of soil mapping units Soil profile description, laboratory analyses and soil classification Soil variability Land evaluation. Socio-economic considerations Selection and requirements of land utilization types Rating of land qualities Estimation of land suitability classes for land utilization types Summary. References.

Interpretation of true colour airphotos. Despite early relatively successful use of aerial colour film, it was only

in the latter half of the sixties that serious attention has been given to

their potentiality. This was primarily due to the insufficient speed and low resolution of the earlier films. Also the high cost and doubt about the value for interpretation played a part. It is argued by those who are in favour of colour photography, that the limited resolution of colour photography when compared with panchromatic photography, is offset by the higher resolution of colours. With colours, an accurate distinction between tones is possible to a degree that is 600 times to 2000 times greater than the distinction in grey tones (Myers, 1968). The value of colour photography for discrimination between objects, therefore, is beyond any doubt (for d'iscrimination between different high chroma soils, the reader is referred to Gerbermann et al., 1971). Although colour fidelity may be low, it is not a limiting factor in the identification of

terrain information (Anson,

1968).

Landform analyses can be

usefully

supplemented by photometric information extracted from colour imagery, such as the ratio Red/Blue revealing differences between soils. For details, the reader

is referred to Piech and Walker (1974).

9.6.

Interpretation of black-and-white Infrared airphotos. Generally, the black-and-white Infrared films offer a good discrimination

between various types of natural vegetation and may emphasize differences in

soil moisture conditions. Since the cost of black-and-white Infrared photography is nearly equal to that of panchromatic photography, the application of this type of film is increasing in tropical forest areas, especially when large areas are concerned.

236

De la Souchere (1966) compared panchromatic films with black- and -white Infrared films in order to find new criteria for delineation of different types of forest in Ctite-d' Ivoire. Small-scale mosaics (1:200.000) -white

Infrared photographs appeared

of black- and

to be a good aid in comparing the

contrasts in Infrared reflection of different types of forest. However, in Ctite-d'Ivoire

the differences between panchromatic and black- and

-white

Infrared as a detecting agent, were found to be variable from one region to the other. At large scale (e.g.

1:3,000),

individual crowns of trees are visible and the

studies may be directed to crown damage (Wolff, 1966). Another application of black- and -white Infrared photography may be found in detecting areas affected by salinity. The crops (e.g. salinity will

cotton) affected by

show a lower reflectance when compared with healthy crops.

However, problems may arise in discriminating between the surface soils and the plants, through which the interpretation may become difficult. Fig. 9.5 enables us to make a comparison between a panchromatic and a black- and -white Infrared aerial photograph of an area at the Surinam river. The panchromatic airphoto was taken in 1953. The black- and -white infrared airphoto was acquired 22 years later when an oilpalm plantation had been founded. Both images show the effect of shifting cultivation. The black- and white -Infrared photograph ha6 high contrast and clearly shows vegetation differences. The dark spots in the plantation may point to places with a moist soil surface.

9.7.

Interpretation of false colour airphotos. The first application of the false colour-film took place in World War I1

when it was used as a detection film for camouflaged military objects. The film is applicable from high altitudes (e.g. 9 km) enabling scales of 1:60.000 up to 1:lOO.OOO.

Owing to the recording of green, red and near Infrared radiation,

the potential of this film for discrimination between soils and vegetation is high. Plants frequently are good indicators of soil condition. Therefore, in case of soils covered by vegetation, the soil scientist has equal interest in detection capability of this film when compared with agricultural and forestry experts. In section 4.2,

the formation of colours in the colour Infrared film

is treated. Below, false colours are discussed briefly.

231

Fig. 9.5.

Panchromatic airphoto (a) and black- and -white Infrared airphoto (b) of the Victoria area at the Surinam river (courtesy CBL Surinam).

238 Dry soils appear in light blue, or light green, and in the case of high organic matter content, in grey colour on this film, while wet soils appear in dark tones. However, grass and healthy broadleaved vegetation are pictured in red to magenta and conifers show dark tones with a slightly magenta hue. Vegetation damage may result in a decrease in near Infrared reflectance and thus leads to an increase in cyan dye and a darker magenta hue. However, plants with yellow unhealthy leaves will appear in white to mauve tones. Knipling (1969) states that many of the colour differences on Ektachrome Infrared aerial photography, particularly the subtle shades of red, can be traced to variations in foliage area, density and orientation, rather than to the reflection properties of individual leaves. When

the reflectance of a plant canopy is compared to that of the single leaf,

there is a striking difference between the canopy reflectance of Visible radiation and that of near Infrared radiation. The canopy Visible reflectance may account for 40%, and the canopy near Infrared reflectance for 70% of the reflectance by a single leaf. The difference will be due to interaction of the radiation transmitted by the toplayers of the canopy with that of the lower leaves. Upon this interaction the Visible radiation is strongly absorbed while the Near Infrared is reflected. The

application

of

false

colour-film

is

reported

in

detection

of

vegetation damage in forested areas (Murtha, 1978) and in urban areas (Remeijn, 1977) as well as in assessment of severity and extent of salt-affected areas in agricultural fields (Myers, 1966; National Academy, 1970). According to Anson (1968), the Ektachrome Infrared film is excellent for soil moisture studies and delineation of vegetation boundaries. Suitable scales are reported for different studies:

-

forestry 1:6,000 and 1:16,000 (Stellingwerf, 1968);

- crown damage in urban areas 1:2,000 or 1:5,000 (Remeijn, 1977);

-

assessment of crop diseases 1:3,600 up to 1:8,400.

For the assessment of salinity problems in growing cotton crops, proper timing of the aerial survey is required. The crops have to be mature and the cotton bolls should not be open. Furthermore, moisture stress will be likely when temperatures and evapotranspiration are high, and irrigation is relatively long ago. Moisture stressed cotton shows less near Infrared reflectance than healthy cotton and produces dark magenta tones on the false colour photographs while cotton plants that are seriously affected by salinity appear as nearly black.

239 Below, an example (see plate 1) of a false colour image of an area in the Netherlands is discussed. Different land use types are clearly marked: planted forest and roadside planting (different colour tones), grassland (bright red to magenta) and arable land (light blueish-green, pink and light red to magenta; note effect of tillage).

Owing to the high reflectance of near Infrared by

grass canopies, red dominates in these places in the picture and differences in grass coverage are masked.

On

the contrary, different canopies of planted

forest and roadside planting show much contrast. At least eight different tree canopies can be recognized by evaluation of colour, size, shape and texture.

While contrast is largest between foliage trees and coniferous trees, this picture

clearly

demonstrates

the

high

potential

of

false

colour

for

differentiating between foliage tree species. To understand colour formation in the false colour image, the various objects can be described visually by their Colour Chart (plate 3 ) .

colour according to the I.T.C.

The colour codes,

obtained in percentages yellow, magenta and cyan, give an impression of the dyes

present

in

the

transparent

film

or

colour

photograph.

percentages are related to the exposure values (see par. 4.2

a.0.

These

dye

fig. 4.9).

However, without quantitative measurements and calibration techniques, the relation is qualitative and rough.

9.8.

Application of multispectral photography. Experiments have been done with multispectral photography (Yost et al.,

1969) to determine its ability for measurement of basic ecological parameters e.g.

unique signatures for species of agricultural crops, trees and soil

surface types. To correct for variables, different techniques are applied (see section 7.8),

for instance man-made targets of known spectral reflectance are

used for calibration, and measurements on illumination and spectral reflectance are carried out. Although results are promising for establishing soil surface types (National Academy, 1970),

application is found mostly in the field of

crop growing. According to Kannegieter (1980), multispectral photography may be applied in order to:

-

gain a better insight into disease behaviour of crops as a basis for more accurate control/prevention;

-

single out in time, likely priority crop areas for preventative/curative action;

- assess damage and yield-reduction

of crops.

9.9.

Interpretation of sequential aerial photography. Interesting

multitemporal

results

about

application

survey are reported by

of

Kiefer

sequential

(1973).

He

repetitive

OK

stated that the

distinction between different soil types was accomplished better by the use of photography of certain dates than by photography of other dates. Consequently, an

optimum

set

of

airphotos

can

be

made

by

selection

from

multidate

photography. Other applications are found in studies on land evaluation, and more specific in erosion studies. Milfred and Kiefer ( 1 9 7 6 ) used sequential aerial photography to study soil variability. They used airphotos taken on 20 different days from May through November 1969 of a corn field in the state of Wisconsin. The photographs were taken from a Cessna 172 aircraft at altitudes ranging from 610 to 1070 m above the terrain. The film types used were: Kodachrome 11 film and Ektachrome InfKaKed Aerof ilm (Kodak type 8 4 4 3 ) . Very little rain had fallen in the area during July, August and September; consequently, the growth of corn during this period was dependent on moisture stored in the soil, the amount of which is largely determined by site, texture and soil depth. The corn grew rapidly where sufficient moisture was available, but turned brown in places where i t was deficient. Dry areas with reduced corn growth were delineated by interpretation of the repetitive airphotos. The dry areas corresponded to slight topographic elevations of 1 to 2 m, with gentle convex slopes. Adjacent nearly-level lower areas did receive runoff from these areas and were relatively moist throughout the summer, enabling better corn growth; the soil depth was found to be the greatest in these lower areas. Thus the crop pattern revealed a dynamic soil property as well as soil distribution. The relationship between crop growth pattern and soil will vary from year to year and from region to region depending on differences in soil profile characteristics, weather conditions and other edaphic factors. Therefore, a careful evaluation of the validity of assumed causive factors is always a necessity. Soil

scientists will

statements about

often

find

it

soil variability without

difficult

to make

quantitative

conducting expensive and

time-

consuming field investigations. Sequential aerial photography offers a tool for evaluation of soil variability and may simultaneously improve the speed and accuracy of mapping. A small format camera mounted on a light aircraft can be

241 used for this purpose. For economic feasibility, the study of seasonal changes may be limited to land units selected from a large study area. Diazo techniques and additive colour techniques (see par. 5.1)

may assist in change detection.

Diazo developing of one band positive transparent materials of two or three acquisition dates in yellow, magenta and/or cyan coloured imagery, forms one of the possibilities. When superposing the diazos of three acquisition dates in yellow, magenta and cyan, the resulting coloured image is interpreted. For imagery with correct colour balance, the interpretation is as follows: black, grey and white indicate no change; coloured places have undergone a change at one or more of the acquisition dates, the colours observed are indicative for change at specific acquisition date(s).

9.10.

Conclusions Black- and -white photographs represent the most common tool for soil

survey by offering a.0. A

low cost stereoscopy.

grouping of airphoto-interpretation units is suggested. When the flow chart

on interpretation for soil survey (see Fig. 8.1) with the suggested grouping (par. 9.2),

is applied, this, together

may lead to uniformity in the legends

of interpretation maps. Fieldwork comprises a.0. boundaries.

Field

checking on validity and accuracy of interpretation

observations may

be

done

guided

by

physiographic

and

morphogenetic interpretation in transects. The interpretation products may be used for preliminary land evaluation which is very useful in the planning of field survey. True colour aerial photography is normally applied at large scales. It is argued that colour fidelity ,which is low when the colour photographs are taken from a high altitude, is not seriously limiting the identification of terrain information. Black- and -white Infrared airphotos offer a good means for discrimination between

vegetation

types

and

clearly

show

differences

in

soil moisture

conditions. Especially in tropical forest areas, application is found for this type of photograph. False

colour

photography

deserves

attention

as

it

offers

a

good

discriminating potential for vegetation types and provides means for assessment of vegetation damage in forest areas, or the severity of salinity as well as the extent of salt-effected areas in agricultural fields. The information

242

presented by the false colours may be described best through its transformation in colour codes, representing percentages of yellow, magenta and cyan.

Multispectral photography i s

generally applied in agricultural remote

sensing projects, but is also promising for soil survey in regions that contain large areas of bare soil. Multitemporal photography may be useful in areas where soil variability is large. 9.1 1.

References

Anson, A., 1968. Developments in Aerial Colour Photogrphy for Terrain Analysis. Photogrammetric Engineering 1968: pp. 1048-1057. Beek, K.J. and Bennema, J., 1971. Land Evaluation for Agricultural Land use Planning. An Ecological Approach. Wageningen, The Netherlands: 47 pp. Bennema, J . and Gelens, H.F., 1969. Aerial Photo-interpretation for Soil Surveys. Lecture notes ITC courses Photo-interpretation in Soil Surveying: 87 pp. Benson, L.A., Frazee, C.J. and Waltz, F.A., 1973. Analysis of Remotely Sensed Data for Detecting Soil Limitations. South Dakota Agr. Exp. Station. Journal Series No 1168. SDSU-RSI-J-73-05: 9 pp. Bergsma, E., 1974. Soil Erosion Sequences on Aerial Photographs. ITC Journal 197413, Enschede, The Netherlands: pp. 342-376. Breimer, R.F., 1976. Detailed Soil Survey of the Rangwe Area. Training Project in Pedology, K i s i i , Kenya, Agric. Univ. Wageningen, The Netherlands: 56 PP. 1973. Land Evaluation for Rural Purposes. Brinkman, R., Smyth, A.J. (ed.), Summary of an Expert Consultation (Chairman: J. Bennema). ILRI, Wageningen, The Netherlands, Publ. 17: 116 pp. Burrough, P.A. and Kool, J.B., 1981. A Comparison of Statistical Techniques for Estimating the Spatial Variability of Soil Properties in Trial Fields, 3Sme Colloque AISS, Traitement Informatiques des Donn6es de Sol (Tome 1 Paris: pp. 29-37. FAO, 1976. A Framework for Land Evaluation. Soils Bulletin, FAO, Rome nr. 32: 72 PP. FAO, 1979. Soil Survey Investigation for Irrigation. Soil Bulletin no 42: 188 pp. Gerbermann, A.H., Gausman, H.W. and Wiegand, C.L., 1971. Color & Color-IR Films for Soil Identification. Photogrammetric Engineering 1971: pp. 359-364. Kannegieter, A., 1980. An Experiment using Multispectral Photography for the Detection and damage Assessment of Disease Infection in Winter-wheat: agronomic considerations. ITC Journal 1980-2: pp. 189-234. Kiefer, R.W., 1973. Sequential Aerial Photography and Imagery for Soil Studies. Highway Research Record 421: pp. 85-92. Knipling, E.B., 1969. Leaf Reflectance and Image Formation on Color Infrared Films. In: Remote Sensing in Ecology; ed. by P.L. Johnson, Athens, Univ. of Georgia Press: pp. 17-29. Milfred, C.J. and Kiefer, R.W., 1976. Analysis of Soil Variability with Repetitive Aerial Photography. Soil Sci. SOC. Am. J., Vol. 40: pp. 553-557. Map Mulders, M.A., 1977. Reconnaissance S o i l Map of Northern Surinam 1:100.000, sheet 13. Soil Survey Department, Ministry of Development, Surinam. Murtha, P.A., 1978. Remote Sensing and Vegetation Damage: A theory for

243

Detection and Assessment. Symp. on Remote Sening for Vegetation Damage Assessment 1978. Publ. by Amer. SOC. of Photogrammetry: 32 pp. Myers, V.I., Asce, M., Carter, D.L. and Rippert, W.J., 1966. Remote Sensing for Estimating Soil Salinity. Journal of the Irrigation and Drainage Division. PKOC. of the Amer. SOC. of Civil Eng, IR 4: pp. 59-69. Myers, V.I. and Allen, W.A., 1968. Electrooptical Remote Sensing Methods as Nondestructive Testing and Measuring Techniques in Agriculture. Applied Optics Vol. 7, No 9: pp. 1819-1838. National Academy of Sciences, 1970. Remote Sensing. With special reference to Agriculture and Forestry. Washington: 423 pp. Nortcliff, S., 1978. Soil Variability and Reconnaissance Soil Mapping: a Statistical Study in Norfolk. The Journal of Soil Science, vol. 29, No 3, Oxford Univ. Press: pp. 403-418. Piech, K.R. and Walker, J.E., 1974. Interpretation of Soils. Photogrammetric Engineering - 1974: pp. 87-94. Remeijn, J.M., 1977. Infrarood Kleurenfilm voor Vegetatiestudies. Landbouwkundig Tijdschrift 89-9: pp. 308-313. SouchSre, P. de la, 1966. Comparaison des Photographies Panchromatiques et Infrarouges dans la Recherche de Renseignements en Zone Forestiere en Cote-d'Ivoire. IIe Symposium International de Photo-Interpr6tation, Paris 1966: 11/59-66. Stellingwerf, D.A., 1968. The Usefulness of Kodak Ektachrome Infrared Aero Film for Forestry Purposes. 11th Congress of the International SOC. for Photogrammetry, Lausanne: 6 pp. Thie, J., 1976. An evaluation of remote sensing techniques for ecological (biophysical) land classification in northern Canada. Proc. of the first meeting Canada Committee on Ecological (Biophysical) Land Classification. 25-28 May, 1976, Petawawa, Ontario: pp. 129-147. Webster, R., 1977. Quantitative and Numerical Methods in Soil Classification and Survey. Clarendon Press, Oxford: 269 pp. Wolff, G., 1966. Schwarz-weisse und falschfarbige Luftbilder als diagnostisch Hilfsmittel fiir operative Arbeiten beim Forstschutz (Rauchschaden) und bei der Waldbestandsdhgung. IIe Symposium International de PhotoInterprgtation, Paris 1966: 11/85-95. Yost, E. and Wenderoth, S., 1969. Ecological Applications of Multispectral Color Aerial Photography. In: Remote Sensing in Ecology edit. by P.L. Johnson, Athens, Univ. of Georgia Press: pp. 46-62. 9.12.

Additional reading.

Beek, K.J., Bennema, J. and Camargo, M., 1964. Soil Survey Interpretation in Brazil. A System of Land Capability Classification for Reconnaissance Surveys. First Draft. DFFS-FA@Stiboka, Rio de Janeiro: 36 pp. Beek, K.J., 1978. Land Evaluation for Agricultural Development. Thesis Agric. Univ. Wageningen, The Netherlands: 333 pp. Bennema, J. and Meester, T. de, 1981. The Role of Soil Erosion and Land Degradation in the Process of Land Evaluation. In: Soil Conservation. Problems and Prospects (ed. by R.P.C. Morgan). John Wiley & Sons, New York: pp. 77-85. Bergsma, E., 1971. Aerial Photo-Interpretation for Soil Erosion and Conservation Surveys. Part 11: Erosion Factors. ITC 9/71, Enschede, The Netherlands: 37 pp. Bergsma, E., 1980. Method of a Reconnaissance Survey of Erosion Hazard near Merida, Spain. Proc. Workshop Assessment of Erosion in USA & Europe (ed. by de Boodt & Gabriels), John Wiley & Sons, New York: pp. 55-66.

244

Bowden, L.W. and BrooneK, W.G., 1970. Aerial Photography, a diversified tool. Geoforum 1970/2, Braunschweig, Germany: pp. 19-32. Breuck, W. de en Daels, L., 1967. Luchtfoto's en hun Toepassingen. E. StoryScientia P.V.B.A., Gent: 176 pp. Bryan, R.B., 1968. The development, use and efficiency of indices of soil erodibility. Geoderma 2: pp. 5-26. Clos-Arceduc, A., 1971. Disposition des Structures D'Origine Eolienne au Voisinage d'un Groupe de Barkhanes a Parcours Limite. Revue "Photo Interpretation, No 2 - 1971, fascicule 1, Editions Technip, Paris. Dudal, R., 1981. An Evaluation of Conservation Needs. In: Soil Conservation Problems and Prospects (ed. by R.P.C. Morgan). John Wiley & Sons, New York: pp. 3-12. Fairweather, S.E., Meyer, M.P. and French, D.W., 1978. The Use of CIR Aerial Photography for Dutch Elm Disease Detection. Symposium on Remote Sensing for Vegetation Damage Assessment, Comm. VII. Int. SOC. for Photogrammetry, Seattle, Washington 1978: 12 pp. Florence, G.R., 1980. Survey and Evaluation of Rangelands in the HukuntsiNgwatle Pan Area, Kalahari, Botswana. ITC, Enschede, The Netherlands (thesis): 141 pp. Foggin, G.t. I11 and Rice, R.M., 1979. Predicting Slope Stability from Aerial Photos. SOC. of her. Foresters, J. of Forestry: pp. 152-155. Fritz, N.L., 1965. Film sees New World of Color. Citrus World 2 ( 2 ) : pp. 11-12, 26.

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